What causes a jerk like a missfire at high speed

What is your question?

We have a 2002 Mercury Mountaineer, It has 104,000 miles on it. We just had a complete tune up done on it. Wires, plugs, gas filter, etc. At no certain time, it will jerk like a miss fire. Usually when cruising down the highway. What could be doing this. Motor or transmission?

What makes this problem better or worse?

its periodically jerking no certain time or speed, usually when just cruising down the road.

How long has your 2002 Mercury Mountaineer had this problem?

noticed it after tune up. but I can't be sure